The objective is to define the ultrastructural cytologic distribution of (Na,K)-ATPase in neurons and glia of the nervous system. Tissues of mouse brain, retina, nerve, and choroid plexus and mouse fetal brain cells in tissue culture will be studied. The catalytic polypeptide of mouse brain (Na,K)-ATPase will be identified by Na ion-dependent phosphorylation, separated from the microsomal fraction by electrophoresis, and used to raise specific antisera. Neurocytologic mapping at the electron microscopic level will be accomplished by means of immunoenzyme staining with peroxidase-antiperoxidase and at the light microscopic level by means of autoradiography with tritiated ouabain. Antisera will be used also to extract holoenzyme by means of immuno-affinity chromatography. Goldfish brain catalytic polypeptide of (Na,K)-ATPase will be obtained for similar purposes.